Mac SE Horizontal Adj Inductor (L2)

[jguay]

I have a Mac SE FDHD that has the screen a bit too wide. I opened it to adjust things and see the variable inductor (L2) is a bit messed up. The hollow core (that a non-conductive hex tool goes inside) has been chipped on the ends and I cannot rotate it to adjust it. I would replace the variable inductor with something new (Digikey or Mouser) but do not know the component values (uH, etc...).

I found the schematics online for the SE, but still cannot find info on this inductor to find a suitable replacement.

Does anyone have any info/guidance on this? Thanks, in advance.

-- Jason

 

[Dennis Nedry]

I would try shoving different sorts of screwdrivers in there from both sides if possible, especially flat ones - maybe you'll find one that will bite into something. You can use metal screwdrivers too, but it will throw off the inductor while it's in there and cause the screen to change size when you take it out. You'd have to guess and check to do it with metal. But there's not much to lose. It's not particularly dangerous especially if you don't directly touch any metal part of the screwdriver.

Another thing you could try is carefully super-gluing a plastic piece inside the inductor being careful not to get any on the inside edges. This would allow you to turn the plastic piece to make the adjustment. This would work best from the component side so that the plastic piece could be left in there and not hit the case when you put it back together.

 

[jguay]

Dennis - Thanks for the input. I'll check into that.

Here are a few pics I took of it. The internal core is hollow and chipped off on the end. As I stated, I tried using a non-conductive hex tool to rotate it, but it won't budge. Also tried a squirt of De-Oxit FaderLube - no dice.

The screen on the Mac SE is too wide (meaning, the mouse goes off the screen on both the left and right sides when booted). My thoughts were to replace the inductor. My problem is I cannot identify the specs of this inductor anywhere and don't know what a "suitable replacement" would be.

Again, thanks in advance for any help.

 

[techknight]

That is the problem with ferrite cores. you have to use a plastic adjuster tool to adjust them. Metal hex tools will crush the ferrite, which appears to have happened at some point.

The only thing you can do is try to find a new core from a junk old radio or something of that nature, and extract it. Smash out the rest of this core and fit in the new core with a PLASTIC hex tool.

You can also attempt to remove the coil assembly from the former assembly and stick down a new former and core over the coil. I used to do this back when I was messing the old tube radios.

 

[jguay]

@techknight - I'm not sure I follow you. I understand about cannibalizing a variable inductor from another device (I already thought of that, but feel like I need to get a variable inductor with the SAME EXACT specs). Can you explain this for me? :

"You can also attempt to remove the coil assembly from the former assembly and stick down a new former and core over the coil. I used to do this back when I was messing the old tube radios."

 

[Dennis Nedry]

Another thing it appears that you could do is cut around the plastic tube with a razor blade and unscrew it off of the chipped inductor core. This will allow you to directly turn the core with your fingers -- with the Mac powered off of course.

I've adjusted these with metal tools - not even carefully - and nothing broke or blew up. It's worth a shot to experiment, and worst case, one of us could figure out the specs of the part for you. You have more to gain than to lose by playing with what you already have.

My next question is - if you bust the core out of there, do you have to replace it with another ferrite core? You could try shoving some other metal pieces in there, screws, etc, it shouldn't hurt anything electrically. There's lots to be learned from these types experiments.

 

[techknight]

You could... BUT the thing you have to worry about is the coil going into meltdown, as a drastic change could cause the core to saturate and melt-down. I dont understand exactly how all that works, its been several years since engineering school.

But as long as its iron based, I dont see why it wouldnt work.

 

[jguay]

OK, so tonight I went ahead and cut away the outer plastic tube around the ferrite core and the core just basically crumbled. So the inductor has no core at all.

@Dennis - Once the crumbled ferrite core was removed I inserted a regular iron screw and powered it up - the display is still "too wide" so I went to adjust the screw and it was hot as hell so I powered off immediately. No harm done to my SE, but seems that inserting a solid metal screw will cause a fire hazard due to the heating up. The SE powers up fine and all, it's just I have no ability to adjust the horizontal width of the display, which is now maxed out on width (since there is NO ferrite core anymore in the variable inductor).

Any suggestions on my next move?

 

[techknight]

I knew that was going to happen about the heat... Its the wrong permeability so it saturated.

You need to try and find a compatible core to fit in. If you can find a cheap junk pocket AM/FM radio, you could grab the old "rod" antenna inside of it and somehow cut it down to size.

Easiest thing to do is keep an eye out for variable inductors on ebay and see if you cant find one to match up to steal a core out of.

 

[Dennis Nedry]

I'm sorry my advice was not very good... But your results are insightful.

Here is a schematic of the analog board (supposedly)

http://web.archive.org/web/20031231184457/http://home.t-online.de/home/andreas.kann/Mac_Power.GIF

However I can't locate L2. I agree that you should probably just look for a new ferrite core.

 

[techknight]

I think thats the macintosh plus power supply.

 

[mcdermd]

Jguay, I'm pretty positive I have a spare, working SE analog board if you want it for the cost of shipping. Send me a PM if you are interested and I'll see about digging it out.

 

[jguay]

@Dennis - you were close - the correct schematic is a few links down from that one on the same web page :

http://web.archive.org/web/20040116004022/http://home.t-online.de/home/andreas.kann/SE_Analogb2.GIF

L2 is close to the center.

 

[Dennis Nedry]

Bummer that it doesn't say anything about it though... I have that awesome Bob Levitus old Mac repair book somewhere, would that say anything about this part? I don't have the book immediately handy, I'll have to find it wherever it's stored away.

 

[techknight]

I wonder if you can use brass as a core? Ive worked on older VT-71s that used brass cores in the tuner circuit.

 

[jguay]

UPDATE - Another board member has offered to send me the part (L2) from a salvage Mac SE. Will update again as things progress.

 

[jguay]

I just received in the mail a replacement inductor (L2) from a fellow board member (THANKS phreakout). Will be installing it this weekend. Thanks for all the bard member input on my issue. Will post a pic of the final results.